Leak detector

ABSTRACT

Apparatus for detecting leaks in fuel storage tanks. A float suspended in the tank liquid determines liquid levels and transmits the liquid level information via an infrared beam to a probe processor in the upper port of the tank. The probe processor stores a plurality of level indications for subsequent uploading to an external computer which analyzes the level information to generate leakage rate information.

FIELD OF THE INVENTION

This invention relates to the provision of apparatus for and a method ofdetecting leaks in storage tanks and, in particular, for detecting leaksin underground tanks that store hydrocarbon products. This inventionfurther relates to a method of collecting and processing data regardingthe leakage rate of underground storage tanks.

BACKGROUND OF THE INVENTION

Leaking tanks and, in particular, leaking underground fuel storage tankspresently pose a significant economic and environmental problem. Thereare thousands of underground fuel storage tanks in use in servicestations and the like throughout the world and, over a period of time,leaks inevitably will occur in many of these tanks. Each leak permitsthe stored hydrocarbons (fuel) to flow into the ground and into thesurrounding environment. Even small leaks are unacceptable since over aperiod of time, a small leak can contaminate a large area and render itunfit for habitation - particularly if it is a residential area. A leakcan also allow ground water to flow into a tank and render the storedfuel unfit for further use. Leaks can also provoke litigation by damagedparties and can result in sizeable damage awards against theowners/operators of the premises on which the leaking tank is situated.Thus, it is most desirable that tank leaks be prevented and/or detectedas soon as possible so that the necessary corrective measures can betaken.

The problem is of such significance that the Environmental ProtectionAgency (EPA) has recently proposed that underground fuel tanks of aproposed date of installation be replaced within ten years. While alltanks have a limited life, a high quality properly installed tank can beexpected to last far longer than ten years. Therefore, while the EPArule might perhaps reduce leakage from some tanks, the ruleunfortunately lumps high quality and low quality tank installationstogether. This penalizes the owner/operators of high quality wellmaintained tanks installation by requiring them to abide by the rulesand regulations that should be applicable only to low qualityinstallations.

The industry is aware of the problem of leaking underground fuel storagetanks and for the most part, is using the best possible availableapparatus to test the tanks currently in use. However, none of thisapparatus is ideal. The ideal tank testing apparatus should meet fiveprerequisites. These are (1) the apparatus should be of sufficientaccuracy to measure the extremely small leakage rates that are requiredfor a tank to meet today's environmental standards, (2) the apparatusmust be easy to use so that it can be installed and operated byrelatively unskilled personnel as opposed to the use of laboratory leveltechnicians, (3) the operation of the apparatus should not interferewith the normal operation of the filling station or facility of whichthe tested tank is a part, (4) the results of the test should not besubject to fraud or manipulation by anyone wishing to alter testresults, and (5) it is also of great importance to eliminate anyoperator adjustments or operator interpretation which could cause errorsas to how the tank is behaving.

It is necessary that the leak detection apparatus be extremely sensitive(it can detect leaks in the range of 0.02 gallons per hour or less) sothat very slight leakages can be detected in a relatively short periodof time. It is extremely difficult to detect the loss (or gain) of 0.02gallons of liquid per hour in a storage tank capable of storing 10,000gallons or more. For example, in a nine foot diameter tank twenty-onefeet long that is half full, the removal of one gallon of gasolinelowers the fluid level 0.00629 inches. The loss of 0.02 gallons per hourwould cause a fluid level drop of 0.0001257 inches or 125.7 micro inchesper hour. It is difficult to measure changes in fluid level of thismagnitude. Also, even when such a change in the liquid level can beaccurately and reliably measured, the change may be due to other factorssuch as a change in fluid density, water table, vapor pockets,vibration, atmospheric pressure, etc. or a change in temperature or byevaporation. This requires that the measurement apparatus, detect andcompensate for the level changes caused by these other factors.

Many of the currently available tank testing devices, while reasonablysensitive and accurate, are complex and require the skills of laboratorylevel technicians in their operation. This precludes the use ofrelatively unskilled personnel and increases testing costs. Also, manyof the currently available testing devices require the placement ofapparatus immediately above the fill pipe area of the tank that is to betested. This is disadvantageous. Tank fill pipes are often situated inthe filling station areas that are used by customers during the normaloperation of the station. The testing of a tank with apparatuspositioned above the fill pipe area requires that portion of the fillingstation to be shut down and made unavailable to the users of thestation. Further, the tank under testing has to be out of service duringthe testing period. This, causes a loss of revenue to the tank owners.And finally, some methods require the tank to be completely full ofproduct (at great expense to the owner) many hours before the start oftesting. Other methods require that the tank be emptied. Some evenrequire the tank to be pressurized. This could damage the tank andcreate a leak by the test procedure itself - certainly if the test wasperformed many times over the life of the tank.

Even if apparatus could be found that meets all of the above mentionedprerequisites, the apparatus would be ineffective if provisions are notmade for safeguarding the integrity of the test data. In other words,there may be instances in which persons may wish to alter the testresults to conceal the fact that a tank is leaking. Obviously, thepurposes of the test are subverted if the integrity of the test resultsis not protected.

Also, the manual logging of any test data by a technician attempting toread/observed minute changes on their instrumentation is not desirable.Many of the known prior art arrangements generate tank leakageinformation at the test site wherein the data is read and/or recordedmanually by the technician for further use. This is most undesirable dueto the inherent reliance of human interpretation of the data derived bysuch instrumentation. Prior systems may record leakage data, but theyare inherently incapable of acquiring accurate data because of the needof interpreting the acquired data and are therefore completelyineffective as a leak detection device. Prior methods and apparatusrequire manual recording and interpretation of tank leakage data on thespot. Since the information is manually recorded, it is subject toalteration or human reinterpretation by persons who might knowingly orunintentionally conceal the fact that a tank is leaking.

It may therefore be seen that it is a problem in the art to provide tanktesting equipment that is accurate in its operation, that can beoperated by relatively unskilled personnel, that does not require humaninterpretation or recording, that does not interfere with the normaloperation of the filling station including the pumping of the testedtank, and that provides for the safekeeping of the test results so as toprevent their alteration either by compromise or by human error.

DISCUSSION OF THE PRIOR PATENTS

The patents discussed in the following numbered paragraphs relate to thedetection of leaks and were uncovered during a prior art search prior tofiling the present application.

1. U.S. Pat. No. 2,054,212 to Bacon of 9-15-36

Discloses an arrangement using a float, a wire, and a drum forindicating fluid levels. The drum is calibrated and the amount that thedrum rotates, as the float and the wire move, provides an indication ofpresent fluid level.

2. U.S. Pat. No. 3,537,298 to Kapff of 11-3-70

Discloses a flow detector for detecting changes in fluid levels.

3. U.S. Pat. No. 3,538,745 to Wright et al. of 11-10-70

Uses a float 72 which detects fluid level changes and generates anoutput signal representing the fluid level. The output signals areapplied to circuitry 18 which drives an indicator 80 representing thecurrent fluid level.

4. U.S. Pat. No. 3,538,746 to Jacobs et al. of 11-10-70

Discloses an arrangement in which the differential pressure on adiaphragm 30 measures the fluid level 44 in a tank 12. A signalrepresenting the fluid level is applied to an indicator device 38positioned above the tank.

5. U.S. Pat. No. 3,805,613 to Stone of 4-23-74

Discloses an arrangement that uses a pool of mercury in a U-shaped tubeto indicate fluid level.

6. U.S. Pat. No. 3,841,146 to Cross of 10-15-74

Discloses an arrangement using external tanks and pumps to detect leaks.This patent discusses the importance of thermal compensation in gas tankmeasurements. For example, one degree of Fahrenheit change intemperature corresponds to an apparent loss of six gallons in a 10,000gallon tank. This is 120 times a leak of 0.05 gallons per hour. TheCross arrangement requires that the tank be filled before the test and aperiod of time is required to circulate the contents of the tank toachieve uniform product temperature.

7. U.S. Pat. No. 4,033,175 to Shiwaku et al. of 7-5-77

Discloses an arrangement that uses a balance element 43 to measure theleakage of gas in a container 28.

8. U.S. Pat. No. 4,186,591 to McOney of 2-5-80

Discloses an arrangement that uses a float 31 together with an indicator59 positioned above the tank to indicate the fluid level within thetank. The arrangement of this patent can only operate when the fluid inthe tank rises into the fill-pipe area.

9. U.S. Pat. No. 4,353,245 to Nicolai of 10-12-82

Discloses an arrangement for monitoring leaks during what is termed thenormal operating conditions of a gas station. This system also detectsthe entry of liquid into a tank from an outside source such as groundwater. The arrangement sets forth a system for measuring fluid levelchanges between equally distant time intervals such as 100 microseconds.It is asserted that the system can detect leaks while pumping is takingplace. The magnitude of the leaks that can be detected by Nicolai duringpumping is not specified.

10. U.S. Pat. No. 4,386,525 of 6-7-83

Uses a capacitance probe 29 to indicate fluid levels. Under theteachings of this patent, the tank is filled with gasoline to a levelwhere the liquid is actually in the fill-pipe. Temperature probes areinserted to compensate for temperature and a capacitive probe isutilized to measure variations in the level changes due to leakage. Thepatent sets forth a separate sensor for determining the lowering of thelevel due to evaporation. By compensating for temperature andevaporation, a more accurate determination of leakage is obtained.

11. U.S. Pat. No. 4,404,844 to Hegler of 9-20-83

Discloses a system in which the pressure on a suspended transducer 10causes output signals to be generated and applied to elements 15 and 16to indicate fluid level.

12. U.S. Pat. No. 4,453,400 to Senese of 6-12-84

Discloses an arrangement for measuring leaks as small as 0.02 gallons ofliquid per hour. The invention makes use of a conventional light source,a photo resistor detector, and a hollow elongated float. The floatengages the fluid in a vertical orientation and utilizes weights tomaintain vertical position. Changes in the level of the tank fluid arebased upon changes in the modulation characteristics of the signal. Afloat 38 moves with changes in the fluid level. A reservoir 44 containsink 19 and a detector 36. The movement of the float controls the amountof ink 19 that covers the detector. This varies the output of thedetector to indicate changes in fluid level within the tank.

13 U.S. Pat. No. 4,505,148 to Zajac of 3-19-85

Discloses an arrangement in which changes in fluid level are detected bya float which produces step output voltage changes indicative of thefluid level changes. The system is proposed to be operated at night whenthe tanks are not being pumped.

14. U.S. Pat. No. 4,532,795 to Brayman of 8-685

Measures the flow of pressurized fluid to a tank to see if the tank isleaking.

15. U.S. Pat. No. 4,571,987 to Horner of 2-25-86

Uses pressure to indicate fluid levels. The system measures temperatureto determine whether fluid level changes are due to temperature changesor due to leaks. A float 40 holds a temperature probe 46. The systemdiscloses a vertical oriented probe extending substantially the entireheight of the tank with the probe being filled with the material havingthe same coefficient of the expansion as the fluid in the tank.

16. U.S. Pat. No. 4,586,033 to Andrejsich of 4-29-86

Discloses an arrangement wherein a number of holes are drilled around astorage tank and floatation sensors are placed in these wells to detectwhether the fluid in the wells is conductive, as is the case for water,or non-conductive, as is the case for gasoline.

17. U.S. Pat. No. 4,604,893 to Senese of 8-12-86

Discloses an arrangement that is similar to the patent described inParagraph 12 above by the same inventor.

18. Reissue U.S. Pat. No. 31,884 to Hansel et al.

Discloses an arrangement in which a sensor 12 weight changes withchanges in fluid level in a tank. The weight change is detected bytransformer 24 and fed to read-out circuitry elements 27 through 29.

It can be seen from the above that a number of arrangements have beenproposed for measuring fluid levels and fluid level changes inunderground tanks. While all of the above discussed arrangements may besuitable for the purposes for which they were conceived, they all sufferfrom one or more disadvantages with regard to the goal of accuratelymeasuring extremely small leakage rates in underground tanks with aminimum of inconvenience to the owner/operator of the tanks and with theuse of relatively unskilled personnel in the operation of the measuringdevices. For example, the arrangements discussed in numbered paragraphs1, 3, 4, 6, 8, 9, 10, 12, 15, 17, and 18 all require the use of complexapparatus immediately over the fill-pipe area of the tank beingmonitored. The use of apparatus immediately over the fill-pipe of a tankis inconvenient and is disruptive to the operation of the fillingstation or facility of which the tank is a part. The reason for this isthat the tank fill-pipes are often in heavy vehicle traffic areas of thefilling station.

It is also most undesirable to take a tank out of service to test fortank leakage. To take a tank being tested out of service means thatfluid cannot be pumped for the duration of the test. The prohibitionagainst testing also includes many hours prior to testing to allow afreshly filled tank to settle with respect to temperature. Also, the useof apparatus of the complexity disclosed by these patents requireslaboratory type technicians making sensitive adjustment subjectivelyrather than relatively unskilled personnel to operate the equipment.

Others of the above discussed arrangements, while possibly beingsuitable for the purposes for which they were originally conceived, areincapable of measuring the relatively small fluid level changes in largeunderground tanks that is required for today's compliance with the laws,rules, and regulations with which today's industry must comply.

It can therefore be seen that it is a problem to provide apparatus thatcan accurately measure small changes in the fluid level of undergroundtanks with the accuracy acquired by today's environment. It is also aproblem to provide apparatus that is not of laboratory complexity andthat can be operated and maintained by relatively unskilled personneland which is cost effective and affordable so tank owner/operators canhave tests performed without having to completely fill the tank or totake the tank out of service and lose revenue during test periods. It isa further problem to generate test data that is not subject tomanipulation by persons desiring to conceal tank leakage information or,erroneous operator interpretation or subjectiveness with respect tointerpretation of instrumentation which inherently relies on humanconclusions.

SUMMARY OF THE INVENTION

The present invention overcomes the above discussed disadvantages andachieves an advance in the art by providing improved apparatus formeasuring fluid level changes in underground tanks. The providedapparatus is accurate and can be installed with a minimum ofinconvenience to the establishment associated with the tank and can beoperated by relatively unskilled personnel. The provided apparatus candetect very small changes in volumetric parameters of fluids inunderground storage tanks. The invention also comprises a method wherebyrelatively unskilled personnel can install, operate, monitor, andmaintain leakage testing apparatus in a plurality of underground tanksconcurrently. The invention is further advantageous in that the providedapparatus, which requires no operator adjustments, can be installed andoperated by personnel who have only a minimal knowledge of theequipment's operation and who have no direct access to the test data.This protects the integrity of the test results.

The provided apparatus is intended for use whenever fluids are stored ineither under or above ground tanks and where it is desirable to easilyand economically test the tanks for leakage while the gas station orfacility associated with the tested tanks continues in operation. Thetesting provided by the present invention may include the testing of anyassociated plumbing that is connected to the tank under test. This canbe done by turning on any connected pumps while not operating or openingany fuel dispenser nozzles. Also, the tank can be tested with any levelof product in it, including up into the fill pipe. It is important tounderstand, that a volumetric method must have some "volume" of productin which to measure, i.e., an empty or near empty tank would beimpractical to test.

The invention further relates to a method for effectively retrieving,processing, and disseminating the data that is obtained from the test.The method of the present invention is implemented by the provision of aplurality of test probes and related equipment on a technician's truck.The technician is responsible for the testing of a plurality of tanksconcurrently. This makes it possible for a single truck and a singletechnician to test many tanks with minimum equipment so as to make thetest affordable. This increases the desirability of frequently testingthe tanks.

A test is initiated at a particular site when the technician unloads theparts of a test probe from his truck and assembles the probe. He thenconnects the probe to a field processor which initializes the probe toprepare it for a test. The technician then removes the cap from thefill-pipe of the tank to be tested, actuates a switch to activate theprobe, and inserts the probe into the tank. The top of the probeincludes a cover similar to the regular cap of the tank fill-pipe. Forexample, the technician would select a 3 inch probe cover to test a tankwith a 3 inch fill pipe. The same probe could be used at a site with 4inch fill pipes by selecting the appropriate size probe cover, etc. Thetechnician departs after he installs the probe which fits fully into thetank and fill pipe and is then free to install test probes in othertanks either at the same or at other sites.

Ideally, the test probe is left in the tank for an extended period oftime, for example, if installed in the afternoon, it is left in the tankover night. The tank fluid level, the temperature and barometricreadings are tested continuously for up to ten hours of data storagewith either an automatic default start time or manual predeterminedstart time. It is important to understand that if the test probe isinstalled for as little as, say, fifteen minutes, the device can detecta leak behavior in the tank. However, the longer the test period, thegreater the "confidence interval" of any voidage rate. Since allacquired data is valid data in the present invention, sudden and largedrops in fluid level that occur are to be attributed to normal depletionof the tank. However, there will be times during which the tank is notbeing pumped. It is these quiet periods that become important when thedata is analyzed later by the program model which interprets thebehavior of the tank. Since the probe test apparatus records all fluidlevel data activity along with temperature and barometric reading andstores these readings in memory organized into "minute logs" and "secondlogs", there will always be a large number of readings representingperiods during which the tank is not being pumped. Therefore, when therecorded data representing (1 ) any detected differences in fluid levelchange, (2) multiple temperature points, and (3) the barometric pressurewithin the tank, are later subjected to the behavioral program model,the results are a determination of a voidage rate (leakage) if oneexists.

A processor on the float device of the present invention dampens any rawlevel data, e.g., vibration due to a passing trucks in the area, or,wind which may blow down the tank's vent pipe, etc. This processorsmoothing is accomplished by an averaging and variance routine andfiltered data is transmitted through the use of an infrared link to thetop of the probe where a second processor organizes the received data,along with the sensed temperature and barometer readings into the abovementioned "second log" and "minute log" format for storage into theprobe memory. Thus, by the end of the test interval such as for exampleover night, the probe has stored enough readings (data points) toprovide a well established assessment of the behavior of the subjecttank.

The technician returns to the test site at the end of the test interval,retrieves the probe from the tank being tested and replaces the originalcap on the tank fill-pipe. The technician then uploads the stored datapoints acquired by the test probe into a field processor. This dataretrieval is accomplished by the technician as he connects the processorportion of the probe to a field processor situated on his truck. He thendisassembles the probe and inserts it into his truck for subsequent useon another test.

The technician later causes the field processor to upload the testinformation (data points) stored in the memory of the probe processor.The memory of the probe processor stores not only the test data, butalso stores permanent information regarding the probe such as the probeserial number, the processor code, and an indication as to how manytimes the probe has been used. All of this information is readout of theprobe processor and stored in the field processor. The truck fieldprocessor also increments a counter in the probe memory by one toindicate the number of times the test probe has been used. Theinformation stored in the truck field processor and pertaining to thetest of a tank is termed to be a test packet.

The technician has a plurality of such test probes on his truck and hemay now move to other sites to deploy a probe in other tanks that are tobe tested. He may also retrieve probes from other tanks that have beeninstalled for a period of time such as over night. The test informationis transferred from each retrieved probe to the field processor in thetechnician's truck. At the end of the technician's schedule rounds, heconnects the field processor to a telephone line via a modem and uploadsthe information stored in the field processor to a regional areacomputer at a central location. This regional area computer merelyrecords tests packets from each tested tank as collected from one ormore field processors. The regional area computer does not generate anytank leakage information. This computer uploads all of its test packetinformation to a national centralized report generation (NCRG) computer.The NCRG computer subjects each test packet to an analysis routine whichdisregards readings associated with sudden drops in fluid levels. Theseare attributed to be due to normal tank depletion due to pumping. Itprocesses the readings taken during quiet periods where small levelchanges may be detected between readings. The data is further subjectedto a model to determine the behavior of the tank based on an analysis ofall pertinent information known. This includes any historical data fromprevious tests performed on the same tank. These modeling techniquesinclude volume integration calculations, thermal conductance, heatcapacities and other expansion coefficient information, tank historyinformation and archival tank mapping trend analysis. This leaves littleconjecture when the NCRG computer prepares the final report as to thevoidage rate for each tested tank.

The test probe comprises a hollow tube which contains a moveable floatassembly in the lower portion of the tube and a probe processor in theupper portion of the tube. The lower portion of the tube is perforatedso as it can receive the tank fluid. The float mechanism floats in thefluid stored in the tank. The movement of the float either up or down,is translated by equipment in the upper portion of the float into codedelectrical signals representing the current level of tank fluid. Thesecoded signals are applied to an infrared LED (light emitting diode)which is positioned in the upper portion of the float. The codedinfrared beam is transmitted upwards within the hollow tube to the probeprocessor in the upper portion of the hollow tube. This associatedequipment includes an infrared detector which receives the coded beamgenerated by the infrared LED. The prob processor converts the receivedinfrared beam into signals representing the instantaneous value of thetank fluid detected by the float. The probe processor periodicallysamples and averages the decoded infrared signals which represent theinstantaneous fluid level within the tank. The results of each sampleare stored in the memory of the probe processor.

The float includes a friction wheel which is vertically oriented so thatthe axis of the wheel is horizontal and perpendicular to thelongitudinal axis of the hollow tube and the float. The friction wheelis rotatable and its periphery is forced against the inner wall of thehollow tube which houses the float. The friction wheel rotates when thefloat moves up or down. The friction wheel is attached by means ofrotational multiplication to a decoder wheel having 500 openings orslots. Each slot extends inwardly radially from the periphery of thedecoder wheel towards the center of the wheel. The decoder wheel ispositioned intermediate a light generator and a light detector in asuitable manner so that a beam of light generated by the light generatoris interrupted periodically as the decoder wheel rotates in response torotation of the friction wheel. The interrupted light signals generatedby the decoder wheel are applied to electronics which generate signalsindicative of the tank fluid level. The signals are applied to theaforementioned infrared LED which generates a coded infrared light beamthat is projected upward to the probe processor in the upper portion ofthe hollow tube comprising the probe.

In partial summary, the float moves up and down in response to changesin fluid level. The float processor also filters out any noise due tovibration, wind, etc. The float processor generates a coded infraredbeam indicative of tank fluid levels. The probe processor receives anddecodes the infrared beam. The probe processor further smooths the rawdata received by averaging and variances techniques and stores theresult in the probe processor memory as minute logs and second logs.

The technician returns to the test site at the conclusion of the test,retrieves the probe from the fill pipe of the tested tank, and connectsthe probe to the field processor in the truck. The field processor readsout (uploads) the contents of the probe processor memory including allof the test data accumulated by the probe processor. For securitypurposes, the field processor also increments a counter within the probeprocessor so that information is always available indicating the numberof times the probe processor and the probe assembly has been used.

The technician then disassembles the probe assembly, stores it in histruck, and moves to another location to test other tanks. The technicianmay immediately connect the field processor via a telephone line and amodem to a headquarters regional area computer which receives the testinformation just retrieved by the technician. Alternatively, thetechnician may retrieve test data from other probes in other tanks in amanner similar to that just described. Then, at the end of the day whenthe technician and his truck return to headquarters, the truck's fieldprocessor may be connected to the regional area computer and theinformation representing all of the tests conducted and retrieved by thetechnician throughout the day may be read out and entered into theregional area computer. This computer then collects data from all suchfield processors within its region and forwards it to the NCRG (nationalcentralized report generation) computer. The NCRG computer then receivesthe test data reported by the various test probes, translates the testdata into tank leakage information, correlates the tank leakageinformation with the leakage history of all tanks stored in the computerand generates the required reports. Further, it stores informationregarding the leakage history of all tanks.

The disclosed apparatus is advantageous and overcomes a number ofdisadvantages of the prior art. First of all, the probe is selfcontained, it is inserted into the tank fill pipe and it is totallyunderground during the testing of the tank. No apparatus is aboveground. This permits the service station of which the tank is a part tocontinue in operation. This is in distinction to many of the abovediscussed prior art patents wherein testing apparatus is positionedimmediately above the fill pipe. This aspect of the present invention ismost advantageous since fill pipes are often situated in the trafficareas of filling stations. The installation of testing apparatusimmediately above a fill pipe would take that portion of the fillingstation out of commercial use for the duration of the test. Further, thetank itself does not need to be out of service as is required by priorarrangements. The present invention allows the tank owner/operator tocontinue business as normal while testing takes place.

Another advantage of the invention is that it only requires the servicesof a relatively unskilled operator to install the probe, to remove theprobe at the end of the test, and to transfer the test data from theprobe processor to the field processor in the technician's truck. Thetechnician's duties do not include the installation or operation ofcomplicated laboratory level equipment with fine subjective adjustmentor interpretation of reading as do prior arrangements. Instead, theinvention requires only the services of a relatively unskilled operatorwho performs no chores regarding the operation of the testing equipmentor an analysis of the data produced by the test. Also, the operator hasno access to the test data that is generated. At the end of the test, hemerely removes the test probe from the tank, transfers the datagenerated during the test from the probe processor to the fieldprocessor on his truck in a form only that the computer understands. Thetechnician then subsequently transfers the test data from the fieldprocessor to a regional computer and then to a national computer whichcontains the software required to translate the test data intomeaningful results including the generation of leakage information forthe tested tank. Since, the field technician does not have access to thegenerated test data, a high degree of security is provided for the testdata and the possibility of fraudulent use or erroneous interpretationof the test data is minimized. For example, since the technician has noaccess to the test data, there is a reduced possibility of collusionbetween the technician and any persons who may wish to falsify data tomisrepresent the integrity of a tested tank. Or, simply due to humanlimitations, manual recording and mis-characterization of values ofinstruments can also misrepresent the integrity of a tested tank. Thisis in contrast to the various prior art arrangements wherein the tankleakage information is derived and displayed at the tank site. In sucharrangements, human frailty can effect the leakage integrity of a testedtank.

It may be from the above that the Applicant's invention provides a newand novel method of testing tanks that overcomes many of thedisadvantages of the above discussed prior art arrangements. It isfurther seen that the apparatus provided to perform the tank testing iscompact, is self contained and is below the fill-pipe cap so as tominimize the inconvenience to the service station of which the testedtank is a part. The method and apparatus of the present inventionovercomes many of the disadvantages of the above discussed prior artdocuments and achieve a technical advance in the art.

DESCRIPTION OF THE DRAWING

These and other advantages and features of the invention may be morereadily understood from a reading of the following description thereoftaken in conjunction with the drawing in which:

FIG. 1 sets forth, in perspective illustration, a fuel tank andassociated plumbing being tested by apparatus comprising one possibleillustrative embodiment of the present invention;

FIG. 2 illustrates the probe of the present invention;

FIG. 3 illustrates further details of the lower portion of the float andthe hollow probe in which the float is contained;

FIG. 4 illustrates the details of the temperature sensing apparatus ofthe probe;

FIG. 5 illustrates the float in the bottom portion of the probe and theequipment in the upper portion of the probe with which the floatcommunicates;

FIG. 6 illustrates the equipment attached to the bottom portion of thefloat;

FIG. 7 illustrates details of the apparatus in the upper portion of thefloat which detects fluid level displacements and generates electronicsignals indicative of such displacements;

FIGS. 8 and 9 disclose further details of the float guide wheels;

FIG. 10 discloses further details of the code wheels and associatedapparatus which generate signals indicative of changes in fluid level;

FIGS. 11, 12, 13, 14 and 15 disclose further details of the apparatus ofFIG. 10;

FIG. 16 discloses the probe processor contained within probe segment 21;

FIG. 17 discloses the probe processor switch and connector looking intothe top of probe segment 21;

FIG. 18 discloses the field processor normally stored in thetechnician's truck;

FIG. 19 discloses the field processor;

FIG. 20 discloses the display panel of the field processor;

FIGS. 21, 22, 23, 24 and 25 disclose further details of the floatprocessor; and

FIG. 26 discloses further details of the probe processor.

DETAILED DESCRIPTION

FIG. 1 discloses apparatus comprising one possible illustrativeembodiment of the present invention being used to test an undergroundfuel storage tank. The tank being tested is shown as comprising a partof a gasoline filling station. Shown on FIG. 1 are an underground tank 1filled to a level 3 with a liquid 2. Further shown on FIG. 1 is a testprobe assembly 4 together with a pipe 5 which permits the fillingstation users to withdraw fluid 2 from the tank 1. Pipe 5 extendsupwards and out of tank 1 to a pump 10 located in a chamber 11 having atop 17A. Fluid 2 is moved by pump 10 through pipe segments 12, 13, and14 to fuel dispensers 18 and 19.

Probe assembly 4 is inserted by technician 16 into the fill pipe 6 oftank 1. The top of the probe 4 is attached to fill pipe cap 7 which ispositioned in an underground chamber 8 having an access fill pipe cover17. FIG. 1 shows the probe 4 already installed in the tank by technician16. Truck 15 is used by technician 16 to transport the test probe 4 andother associated test equipment from location to location. FIG. 1 alsoshows the bottom of tank 1 having a small crack 20 through which fuel 2may escape from the inside of the tank to the outside environment (orthrough which water from the ground may flow in).

It should be noticed in connection with FIG. 1, that the entirety of thetest apparatus of the present invention is contained within probe 4 andthat this apparatus is unobtrusive and below the top surface theconcrete slab 9 of the filling station. Since the probe is underground,it permits the tank to be tested in a manner that does not interferewith normal operation of the filling station of which the tank is apart. It also does not require laboratory level technicians to operatethe equipment.

DESCRIPTION OF FIG. 2

FIG. 2 discloses further details of probe 4 of FIG. 1. The probecomprises an upper segment 21 which is attached to the bottom of fillcap 7. The probe 4 further comprises a lower segment 22. Attached to thebottom portion of probe segment 22 is a bottom cap 23 which, as shown onFIG. 3, has a knurled portion 24, drain holes 25, and a conical shapedbumper member 26. The probe 4 further comprises a tape or strip 27having a plurality of temperature detecting elements (such as everyeight inches) shown as dots 29 on FIG. 2 atop the strip 27. Elements 29are each connected by separate conductors to a probe processor withinsegment 21 which records the temperature of the tank fluid at differentlevels as well as the temperature of the vapor above the tank fluid atdifferent levels.

In operation and in accordance with the teachings of the presentinvention, the technician 16 measures the depth of the fluid 2 withintank 1 at the test site by the conventional dip stick method, not shownin the drawing. That is, distance between the tank bottom 1A and thefluid surface 3, as well as the distance between the tank bottom 1A andthe top 6A of fill pipe 6. These dimensions are entered into the fieldprocessor 108 (FIG. 19) wherein the field processor recommends theappropriate length probe 4 to use in testing tank 1. This process alsoeliminates the possibility of testing an empty tank. It should be notedthat although this function is a human judgment with respect to levels,it is in no way a factor in the determination of whether the tank isleaking. After selecting the appropriate length probe 4 which is storedin truck 15, the technician 16 assembles the apparatus by firstactivating the float processor 59 (FIG. 7) and inserting the float 30into the hollow inner portion of the probe member 22 through the bottomas shown in FIG. 3. A plug 23 is then attached to the bottom portion ofprobe segment 22 to captivate the movable float 30 within the hollowchamber of segment 22.

Next, technician 16 connects a conventional RS232 communications typecable (not shown) between the probe processor 48 which is housed withinthe upper segment 21 via connection 107. The field processor 108 promptsthe technician to activate the probe processor 48 by positioning switch106 to ON as shown in FIG. 17.

The field processor 108 initializes the probe processor 48 to do a selfdiagnostic routine which includes all aspects of operation such asbattery life, memory, temperature sensors, and communication. The floatprocessor has already been activated as previously described. If allfunctions are okay as determined by the field processor 108, thetechnician 16 is prompted to disconnect the RS232 communications cableand install the probe 4 in tank 1. He next affixes probe 4 and its uppersegment 21 to the bottom of fill cap 7. Fill cap 7 is selected atvarious tank sites to fit a variety of fill pipe 6 sizes. In thismanner, the probe 4 can easily accommodate any tank. The probe isinstalled into the tank 1 by inserting the properly activated probe 4 infill pipe 6 until the bottom of the fill cap 7 rest on the top 6A offill pipe 6. A lock may be conventionally installed on the test probe 4fill pipe cap 7 in the same manner as would be installed on anyconventional fill pipe cap. The fill pipe manhole cover 17 is put backin place and the technician 16 has completed this portion of the tanktesting operation and is free to leave the test site.

The probe 4 contains a movable float element 30 (shown on FIGS. 3 and 5)which is contained within the hollow inner portion of the probe member22. The float 30 is inserted into the bottom portion of lower probesegment 22 and is captivated within by the bottom plug 23 to the bottomportion of probe segment 22. Drain holes 25 and 34 (FIG. 3) in segment22 permit the tank fluid 2 to enter and fill the inside of the probeassembly 4. Float element 30 (FIGS. 3 and 5) floats in the fluid 2inside the hollow segment 22 to the exact up or down movement of floatelement 30 with changes in tank fluid levels and permits the probe todetermine the tank fluid level at any time during the test.

The knurled portion 24 of bottom plug 23 (FIG. 3) facilitates assemblyand disassembly of the probe assembly. Float element 30 containsapparatus for generating signals indicating the fluid level in the tankat all times during the test. These signals are transmitted upwardswithin probe 4 by means of an infrared beam 44 to a probe processor inthe upper segment 21 of the probe. The probe processor responds to theinfrared signals, samples the signals periodically and storesinformation pertaining to each sample within a memory element associatedwith the probe processor.

Petroleum based fluids are subject to considerable expansion andcontraction as the temperature of the fluid varies. These contractionsand expansions result in changes in fluid level of a degree that canequal or exceed the differences in fluid levels caused by small tankleakages. Therefore, it is necessary that the tank fluid temperature besensed at all times and that fluid temperature information be suppliedto the probe processor which also determines the tank fluid level fromthe received infrared signals.

FIG. 2 illustrates elongated strip 27 which extends downwardly along thefiberglass probe segment 22. Strip 27 is attached to the probe segment22 by means of a suitable bonding material, such as fiberglass andepoxy. Strip 27 includes a plurality of temperature sensing elements 29(such as every eight inches). The probe processor, continuously receivesand records this information from elements 29 together with the fluidheight information received from the infrared beam 44 generated by thefloat. The probe processor records the tank fluid level information andalso records the fluid level temperatures generated by the variousdevices 29. In addition, a pressure sensor resides on the probeelectronics processor printed circuit board 48 inside the upper probesegment 21 and is common to atmosphere within the tank 1 and fill pipe6. This indicates to the probe processor 48 the barometric pressure.These values are recorded along with the above mentioned level andtemperature values. In the present embodiment, the probe processor doesnot perform the calculations that would be required to integrate thefluid temperature and barometric pressure information with the fluidlevel information so as to generate meaningful information indicatingthe extent to which the tank may be leaking. Instead, the probeprocessor merely records the temperature barometric pressure and fluidlevel parameters for each reading and makes this recorded informationavailable to a field processor in the technician's truck at the end ofthe test interval.

DESCRIPTION OF FIG. 3

FIG. 3 discloses the bottom portion of probe segment 22 together with aportion of float 30 which is contained within the interior of probesegment 22. The technician inserts float 30 into the hollow segment 22at the beginning of a test and then attaches bottom plug 23 to thebottom portion of segment 22 by means of threads 37 on plug 23 andcooperating female threads on the bottom end of element 22.

Attached to the bottom portion of float 30 is tubular member 31 havingspring 32 affixed to its bottom end. Spring 32 isolates probe 30 fromshocks that otherwise might be encountered if element 31 would hit thebottom inner portion of plug 23. This could occur when the probe isfirst positioned in a vertical position prior to inserting it into thefill pipe 6 of the tank to initiate a test.

Affixed to tubular member 31 are three wheels 35 which are positionedcircumferentially approximately 120 degrees from each other with respectto the longitudinal axis of the member 31. Wheels 35 are spring loadedand bear against the inner wall of probe segment 22 when float 30 isfully inserted within segment 22. Wheels 35 center float 30 within theinner portion of segment 22 in such a manner that float 30 does not rubagainst the inner surface of segment 22. Wheels 35 and similarlyarranged wheels 39 (shown on FIGS. 5 and 7) on the top portion of float30, keep float 30 freely movable within the inner portion of hollowelement of probe segment 22. Float 30 is hollow and it is free to floatup or down within the hollow probe segment 22 in the tank liquid at theexact level of the tank liquid. The height of float 30 within the liquidat any time is indicative of the current fluid level within the tank. InFIG. 5, fluid level 3 shows where float 30 sets in the liquid. Thisrelationship may be higher or lower depending on the specific gravity ofthe fluid being tested.

Bottom plug 23 has holes 25 in its bottom surface. Holes 25 permit tankfluid to drain from probe segment 22 at the end of a test when probe 4is removed by the technician from the tank. Hole 34 in the lower portionof segment 22 also facilitates the removal of any tank fluid from theprobe at this time.

DESCRIPTION OF FIG. 4

FIG. 4 discloses further details of strip 27 and its temperature sensingelements 29. FIG. 4 illustrates three separate portions of segment 22.The upper portion of strip 27 emerges from an opening 28 in the upperportion of probe segment 22 and extends downwardly along the outerperiphery of the probe to the bottom portion as shown on FIG. 2. Strip27 contains a plurality of separate electrical conductors 40 togetherwith a plurality of temperature sensing elements 29. Each temperaturesensing element 29 has two terminals which are connected to a differentpair of the conductors 40. Strip 27 includes an outer coating 45 whichis applied to the strip after the temperature sensing elements 29 areattached to the various conductors 40. The conductors 40 and temperaturesensing elements 29 are then encapsulated by coating material so as toprotect the conductors 40 and elements 29 from the corrosive effects ofthe tank fluid. The strip 27 is affixed to the probe assembly by meansof a suitable bonding material such as for example, epoxy cement andfiberglass cloth.

Strip 27 enters opening 28 at its upper end and within segment 22 isconnected to processor within segment 21 which derives temperatureinformation for each of elements 29. A second temperature strip 36 alsoextends out of opening 28 and extends upward along element 21 (see FIG.2), through the fill cap 7 where it is connected to a probe 38 which canbe inserted into the soil of chamber 8 to measure the soil temperature.Strip 36 also includes temperatures sensing elements 29 for sensing thetemperature of the vapors above the fluid within the fill pipe 6.

FIG. 5 illustrates the major components comprising probe 4 together withthe manner in which these components interact to monitor the fluid levelin the tank in which probe 4 is inserted. As can be seen from FIG. 5,probe 4 includes a fill pipe cap 7 on its top portion and an upper probesegment 21 whose top end receives the threaded portion of the fill pipecap 7. Probe 4 further includes a lower probe segment 22 and a bottomplug 23 having a rubber bumper 26 and a knurled portion 24. Threads 37of the plug 23 permit the plug to be screwed into mating female threadson the bottom portion of lower probe segment 22.

Probe segments 21 and 22 are hollow and probe segment 22 contains thefloat 30 which was inserted into the bottom of segment 22 by thetechnician prior to screwing bottom plug 23 into the bottom of probesegment 22. Tubular member 31 is attached to the bottom of float 30 andwheels 35 are attached to the outer surface of tubular member 31. Spring32 on the bottom of member 31 cushions the float 30 in the event that itshould drop suddenly against the bottom of plug 23. Wheels 35 bearagainst the inner surface of probe segment 22 and keep float 30 centeredand away from the inner walls of segment 22. Tubular member 52 isattached to the upper portion of float 30 and wheels 39, which aresimilar to wheels 35, are attached to the outer surface of member 52.Wheels 39 and 35 work in combination to keep the float centered withinand away from the inner walls of lower probe segment 22 while at thesame time permitting the float 30 freely to move up and down as the tankfluid level changes.

Attached to the top of tubular member 52 is the apparatus generallydesignated as 41 which continuously generates information indicating theheight of the fluid in which float 30 is suspended. The details ofapparatus 41 are subsequently described in connection with FIGS. 7 and10. The output information from apparatus 41 is applied to floatprocessor 59 shown in connection with FIG. 7 which generates signalsthat are applied to the infrared light emitting diode (LED) 43. LED 43generates a coded infrared beam 44 which is transmitted upwards withinprobe segment 22 to the infrared photo detector 47 shown within springs46. The output of photo detector 47 is extended upwards and overconductors 53 to the probe processor generally designated as 48 in FIG.5. Processor 48 is shown as being contained within upper probe segment21.

It may be seen from the above that float 30 moves up or down, as thecase may be, in response to corresponding changes in the level of thetank fluid in which probe 4 is suspended. The apparatus 41 detects eachmovement of float 30 in response to each change in fluid level andgenerates a continuous signal at all times indicating the tank fluidlevel. Since the output of apparatus 41 is connected by associatedelectronic equipment to the infrared LED 43, LED 43 generates andprojects upward a coded infrared beam containing information specifyingthe instantaneous value of the tank fluid level measured by apparatus41.

The coded infrared beam is received by photo detector 47, passed overconductors 53 to the probe processor 48 which continuously samples thefluid level information received via the infrared light beam. Thesampled fluid level information is temporarily stored in a scratch padmemory of the processor. The processor analyzes the stored informationto produce tank fluid level information that is usable for subsequentprocessing operations. For example, the processor disregards informationassociated with sudden drops in tank fluid level since these are assumedto be due to normal depletion and not to tank leakage. Also, theprocessor disregards ten percent of the readings representing the lowestfluid level and ten percent of the readings representing the highestlevel. It then averages out the remainder of the readings to generate aresultant figure representing the tank fluid level for a given intervalof time such as for example every second. In other words, once everysecond the processor generates a figure that represents the averagelevel of the fluid within the tank for the one second interval. This onesecond fluid level reading is then stored in a semi-permanent area ofthe processor's memory and remains there until a 30 second mark occurs.Every 30 seconds, a least squared algorithm is applied to the previous29 second values. The resultant slope along with the 30 second levelvalue, 16 temperature values from elements 29, and the barometricpressure value are stored in a permanent area of processor memory toremain there until the information is read out by the technician's fieldprocessor.

The operation continues in this manner for the duration of the test withthe probe processor 48 generating fluid level, multiple temperature andbarometric pressure data points and storing this information forsubsequent readout in the semi-permanent memory of the probe processor.Finally, the technician returns to the site of the test at the end ofthe test and lifts the entire probe assembly 4 as shown on FIG. 5 out ofthe tank. He unscrews the fill pipe cap 7 from probe segment 21 in orderto gain access to the switch 106 and the connector 107. He then connectsa field processor on his truck, as subsequently described, to theconnector 107 and operates the field processor to cause the contents ofthe memory of probe processor 48 to be transferred from the probeprocessor to his field processor. The information regarding the resultsof the test is then stored in the field processor and made available forsubsequent transportation back to the NCRG computers.

The "test packets" (logs) are transported back to the NCRG center forfurther processing. As each log is received, the raw digital values areconverted to physical units (e.g., degrees Fahrenheit) and then passedonto a mathematical model along with other parameters. Incorporatedwithin the embodiment of this application are means for precise fluidlevel, temperature and ambient pressure recording; means for on-probepreprocessing of the digital signal; means for transporting loggedsensor readings; means for mathematical simulation of a non leakingtank, and finally means for expression of the test results. Test resultsare generated reporting statistical history of the tank and thengraphically displaying logs and model output over time. These graphsinclude: (1) fluid level temperature and pressure data points, (2)uncompensated and compensated tank volumes, and (3) uncompensated andcompensated voidage rates, and finally voidage rate in gallons/hour witha specified "confidence interval" as a percentage from 1 to 100.

The information that is generated and stored by the probe processor 48includes not only the tank fluid level information but also thetemperature information at various levels of the fluid. This informationis generated by various elements 29 of strips 27 and 36 which have beendescribed in detail in connection with FIG. 4 and therefore are shownonly generally in connection with FIG. 5. Strip 27 and its associatedelements 29 generates the temperature information for the lower portionof probe 4. Strip 36 and its associated elements 29 generate thetemperature information for the upper portion of the probe. The opening28 and the lower hole 34 in element 22 (FIG. 3) together with the holes25 in plug 23 permit the tank fluid to enter the probe assembly 4 whenthe probe is first inserted into the tank. These holes and openings alsopermit a change in the level of the tank fluid to reflect acorresponding change of the fluid within the inside of probe 4. Thus,float 30 responds to all changes in tank fluid level so that the levelof float 30, and the coded infrared information transmitted upwards inlight beam 44, at all times reflects the instantaneous level of thefluid within the tank. These holes and openings also permit the fluid todrain readily from the inside of probe 4 when it is removed from thetank at the end of the test.

The technician disassembles the probe by unscrewing lower plug 23,removing float 30 from the bottom of the probe. The various elementscomprising the probe are then stored on the truck by the technicianfollowing the disassembly of the probe 4. Following the disassembly ofprobe 4 and the reading out of the information from the probe processor48 into the field processor stored on the truck, the technician is freeto proceed with the testing of other tanks, either at the same locationor at another location.

DESCRIPTION OF FIGS. 5, 6 AND 7

FIGS. 5, 6 and 7 disclose further details of the float 30, the apparatusconnected to the bottom of float 30 and the apparatus connected to thetop of float 30. FIG. 6 discloses a bottom segment of float 30 togetherwith further details of the apparatus connected to this portion of float30. As can be seen on FIG. 6, the tubular member 31 is connected to thebottom portion of float 30 by means of threads 56 on the upper portionof member 31 and by means of cooperating female threads (not shown) inthe lower portion of float 30. Three guide wheels 35 are mounted totubular member 31 as generally indicated on FIG. 6 and as described indetail on subsequent figures. The purpose of these three wheels is tocenter float 30 within the inner confines of probe tube 22 while at thesame time preventing float 30 from contacting or rubbing against theinner wall of probe segment 22. The wheels 35 are low friction devicesmade for example of Teflon and freely permit the float 30 to move up ordown in response to changes in tank fluid level.

Springs 32 are mounted on fixture 54 which in turn is affixed to thelower portion of tubular member 31 by means of threads 64 andcooperating female threads (not shown) in the bottom of tubular member31. The function of springs 32 is to cushion float 30 and the apparatusconnected thereto from the shocks that might otherwise be encountered inthe event that the bottom of tubular member 31 and float 30 should movedownward suddenly and bump up against the bottom inner portion of lowercap member 23.

FIG. 7 shows the top of float 30 in segmented form together with furtherdetails of the apparatus connected to the top portion of float 30. Thefunction of the apparatus mounted on the top of float 30 is to detectchanges in tank fluid level, to generate information indicating thecurrent level of the tank fluid and to generate a coded infrared signalthat is transmitted upwardly within lower probe segment 22 indicatingthe current level of the fluid within the tank being tested. Theapparatus that detects changes in fluid level is generally designated as41 on FIG. 5. On FIG. 7, this apparatus includes a friction wheel 60, acode wheel 57, and a pick-up transducer 56. Apparatus 41 is mounted tothe top of a tubular member 52 with the bottom portion of tubular member52 being affixed to a threaded member 67. The threaded member 67 iscooperates with female threads (not shown) on the top inside portion offloat 30. The two guide wheels 39, shown on FIG. 7, serve both the samefunction as do the lower guide wheels 35. They also position the float30 so as to insure continuous contact of the friction wheel 60 with theinner wall of the probe 22. Wheels 39 are mounted to tubular member 52by means of apparatus that is discussed in detail subsequently.

Apparatus 41 includes a friction wheel 60 whose outer periphery bearsagainst the inner wall of probe tube 22 and maintains continues contactaided by the wheels 39. Wheel 60 is rotated in response to verticalmovements of float 30 and the rotation of wheel 60 causes a rotation ofcode wheel 57. Code wheel 57 contains a plurality (500) of radial slotsor openings, in the preferred embodiment, in its outer periphery and theouter portion of code wheel 57 is positioned within the lower U-shapedopening of transducer 56. Code wheel 57 and transducer 56 areconventionally available from Hewlett-Packard Corporation, 370 WestTrimble Road, San Jose, Calif. 95131 as part numbers HEDS-5100-A03 andHEDS-9100-A00 respectively. Transducer 56 contains a light source and alight detector positioned on opposite sides of the code wheel 57. Theslots within code wheel 57 alternately enable and break the light beamgenerated by the light source and received by the photo detector. Theseinterruptions are detected by the photo detector, converted to theappropriate electrical signals by transducer 56 and applied out overconductors 53, through the inner portion of tube 58 downward through thelower inside portion of threaded element 67. These electrical signalsare applied to float processor 59 which process these signals andgenerate an output signal which is applied by means of conductors 61 oftube 58 to the infrared light emitting diode (LED) 43 which ispositioned within the top portion of cone 42. The electronics apparatus59 applies coded signals to the infrared (LED) 43 indicating the currentinstantaneous level of the tank fluid in which float 30 is floating.Cone 42 is mounted to the outer walls 68 of apparatus 41 by means ofscrews 66. Its cone shape is important to shed condensation which mayresult from the vapors above the fluid in which float 30 is floating.Condensation droplets may add weight to the float and thus the floatwould ride lower in the fluid and give error to the fluid level value.

In summary with regard to the apparatus shown in FIGS. 5, 6 and 7, thefunction of this apparatus is to keep the float 30 centered within probesegment 22, detect the instantaneous level of the tank fluid in whichfloat 30 is suspended to generate signals indicating the tank fluidlevel, and to generate a coded infrared beam which contains informationrepresenting the instantaneous value of the level of the tank fluid.Friction wheel 60 engages the inner wall of probe segment 22 and isrotated in response to vertical displacements of float 30. Each rotationof wheel 60 causes a rotation of code wheel 57 which, in turn, causesthe electric signals to be generated that specify the instantaneouslevel of the tank fluid. The electronics equipment 59 is affixed bymeans of a bracket 63 to a bracket 62 and is totally contained withinthe inside of float 30 when threaded member 67 is threaded into thefemale threads in the upper portion of float 30.

DESCRIPTION OF FIG. 10

FIG. 10 discloses further details of the apparatus 41 comprising thefriction wheel 60 and the code wheel 57. Apparatus 41 includes acircular base member 69 having two cut-out portions for receiving thebottom portion of vertical walls 68. The left wall 68 on FIG. 10 ismounted to the cut-out portion of base 68 by means of the three screws71. The right wall 68 is mounted to base member 69 in a similar manner.A jeweled bearing plate 81 is affixed by means of screws 72 to the innerportion of each wall 68. Similarly, a jeweled bearing plate 80 isaffixed by means of screws 73 to the inner surface of each of wall 68.

Friction wheel 60 has a shaft 78 and the ends of shaft 78 are mountedwithin jeweled bearings in plates 81. Similarly, code wheel 57 has ashaft 79 with the ends of shaft 79 being mounted in jeweled bearings inplate 80. Elongated holes 72A allow plates 81 to be positioned such tocorrect any machining tolerances during manufacturing so as to adjustthe minimum amount of tension between the friction wheel 60 and codewheel shaft 79.

Spacers such as spacer 82, are mounted by screws 74 to walls 68 so as tokeep the two walls 68 the proper distance from each other. The pick-uphead 56 is mounted against the right wall 68 by means of screws 83 andnuts 84. As shown on FIG. 7, pick-up head 56 has a bottom U-shapedopening into which the outer portion of code wheel 57 is positioned. Thecode wheel 57 has radial slots or openings 70 circumferentially arrangedand pick-up head 56 includes a light source and a light detector whichcooperate with the slots 70 and code wheel 57 to generate tank fluidlevel information.

The circumference of wheel 60 bears against the inner wall of probe tubesegment 22 and wheel 60 is rotated in response to each up and downmotion of float 30. A rotation of wheel 60 rotates wheel 57 since thecircumference of wheel 60 bears against shaft 79 which acts like apulley to amplify the motions of wheel 60 by a factor corresponding tothe corresponding diameters of shaft 79 and wheel 60. As a consequence,code wheel 57 is rotated in response to each rotary movement of wheel 60and the rotation of wheel 57 causes its slots 70 to alternatelyinterrupt and enable the light beam generated by pick-up mechanism 56.The output signals from pick-up mechanism 56 are applied over the fivepins 85 which are inserted into corresponding sockets of plug 86 whichis connected to wires 53. Thus, the output signals from pick-up head 56are applied over conductors 53 extend downwardly through tube 58 andthrough threaded element 67. The lower end of these wires is connectedto the float processor circuitry 59 shown on FIG. 7 by connectors 62 and63. Processor 59 is connected to the bottom part of threaded element 67and is totally contained within float 30 when threaded element 67 isscrewed into the female threads in the upper portion of float 30. Setscrews 76 and 77 affix wheels 60 and 57 respectively to shafts 78 and 79respectively. Retainer screws 75 hold wheel 57 on drum 98.

The three wheels 39 are connected to the tubular member 52 by means ofthe indicated apparatus shown on FIG. 10. This apparatus includes a flatspring member 88 having an outer end to which each wheel 39 isconnected. The inner or lower portion of each of flat spring member 88is connected by means of a screw 87 to the outer wall of tubular member52. The subsequent figures show further details of the apparatus andhardware used to mount wheels 39 and wheels 35.

DESCRIPTION OF FIGS. 8 AND 9

FIG. 8 comprises a cross-sectional view taken along line 8--8 of FIG. 6and looking upwards from line 8--8. Shown on FIG. 8, is the bottom offloat 30 contained within the wall 22 of the lower section of probeelement 22. Float 30 is kept away from and centered within the innerconfines of probe segment 22 by the three wheels 35 which are spacedapproximately 120 degrees from each other. The three wheels 35 aremounted by the springs 88 and means of the indicated screws to a cut-outin tubular element 31 which is attached to the lower end of floatelement 30. As seen on FIG. 8, the three wheels 35 keep the float 30centered within the probe element 22 while at the same time permittingthe float element 30 to easily move up and down as the case may be asthe tank fluid level changes.

FIG. 9 comprises a cross-sectional view taken along line 9--9 of FIG. 7and looking upwards from line 9--9. Shown on FIG. 9 are the two wheels39 which are attached by means of the indicated spring members 88 to theupper tubular element 52. The lower end of element 52 is attached tothreaded element 67 (FIG. 7) which, in turn, screws into the upper endof float 30.

In a manner analogous to that of FIG. 8, wheels 39 keep the floatelement 30 centered within and away from the inner walls of probeelement 22 while keeping continuous pressure on the friction wheel 60 bymeans of the spring 88. These two wheels 39 assure contact of thefriction wheel 60 to the inner wall of probe element 22. At the sametime, the wheels 39 permit the float element 30 to easily move up ordown when changes occur in the level of the tank fluid.

DESCRIPTION OF FIGS. 11 AND 12

FIGS. 11 and 12 disclose the apparatus used to mount wheels 35. On FIG.11 this apparatus is shown as comprising a flat spring 88 together witha wheel frame 89. The wheel frame 89 is shown on FIG. 11 in its unbentform. In its fabrication, the wheel frame 89 is bent by 90 degreesdownward in the area of each of the indicated dotted lines. Theresultant configuration of element 89 is shown in FIG. 12 where itcomprises an inverted U-shaped form with the one end of spring element88 being affixed to the upper portion of element 89 by any suitablemeans such as spot welding. Wheel 35 comprises a wheel frame 95 made ofTeflon and a tire 94 mounted in the circumferential grooves of wheelframe 95. The wheel frame 95 has a center hole to receive a bolt 92. Thewheel 35 is mounted and contained within the U-shaped portion of element89 by aligning the hole in wheel frame 92 with the holes 91 in element89 and then by inserting the bolt 92 through the first hole 91, throughthe hole in the wheel frame 95 and then through the second hole 91 ofelement 89. Bolt 92 is held in place by the snap ring 93.

After being fabricated in the manner shown in FIG. 12, the outer end ofthe spring member 88 is bent slightly as shown in FIG. 10 and the hole96 of spring member 88 permits spring member 88 to be affixed to thetubular element 52 as shown in FIG. 10. The wheels 39 as shown in FIGS.10, 9 and 7 are mounted by similar apparatus to that shown in FIGS. 8, 6and 3 for wheels 35.

DESCRIPTION OF FIGS. 13, 14, AND 15

FIG. 13 discloses the apparatus used to mount the shafts 78 and 79. Ascan be seen on FIG. 13, this apparatus includes a left wall element 68of the wheel assembly 41, a right wall element 68, an upper bearingplate 80 in each wall 68 and a lower bearing plate element 81 in eachwall 68. The ends of axle 78 are mounted in jeweled bearing surfaces ofbearing plates 81 while the ends of axle 79 are mounted in jeweledbearings in bearing plates 80. The friction wheel 60 is mounted on shaft78 as shown on FIG. 10. Wheel 60 is rigidly affixed to shaft 78 by meansof set screw 76. The code wheel 57 is mounted on shaft 79 and is affixedto the wider left hand portion of shaft 79 as shown on FIG. 13 by setscrew 77.

FIG. 14 discloses further details of the apparatus associated withshafts 78 and 79 of FIG. 13. FIG. 14 also comprises a cross-sectionalview taken along lines 14--14 of FIG. 7. FIG. 14 shows the shafts 78 and79 having their ends mounted in the jeweled bearing surfaces in a leftwall element 68 and in a right wall element 68. FIG. 14 further showshow wheel 60 and its drum 97 is mounted on shaft 78. FIG. 14 also showsin detail how code wheel 69 and its drum 98 are mounted on shaft 79. Therotation of friction wheel 60 in response to the up and down motions offloat 30 causes shaft 79 and code wheel 57 to rotate since thecircumference of friction wheel 60 bears against the thin portion ofshaft 79 so that a rotation of wheel 60 causes an amplified rotation ofshaft 79 and code wheel 69. FIG. 14 also shows the two centering wheels39 which through the spring 88 causes the float 30 to make continuouscontact of the friction wheel 60 with the inner wall of the probeelement 22 as well as a cross-sectional view of tube 58 containing thewires 61 and 53.

FIG. 15 comprises a cross-sectional view taken along lines 15--15 ofFIG. 7 and shows how the wheel assembly 41 operates when positionedwithin the inside of probe element 22. Shown on FIG. 15 is element 69upon which is mounted the vertical wall element 68. Wall element 68receives one end of shafts 78 and 79 with wheel 60 being mounted onshaft 78 and with wheel 69 being mounted on shaft 79. The circumferenceof wheel 60 bears upon the inner wall of probe element 22 and also bearsupon the axle 79. Thus, when wheel 60 rotates as the float movesvertically, an amplified rotation of shaft 79 and wheel 69 results. Theupper portion of wheel 57 is positioned within an opening in pick-upelement 56 and the slots or cut-outs 70 in wheel 57 causes sequentialinterruptions of a light beam within pick-up element 56. These signalsresulting from these interruptions are applied to the pins 85 of pick-upelement 56. Pick-up element 56 is mounted by nut 84 and bolt 83 to wallelement 68. The signals on pins 85 of pick-up element 56 are extendedthrough cooperating female pins and plug 86 and over the five wires 53to the electronics facilities 59 which, as shown on FIG. 7, are attachedto the bottom portion of threaded element 67 and which are containedwithin the inner top portion of float element 30 when the threadedelement 67 is screwed into cooperating three female threads in the upperportion of float element 30. The wires 53 on FIG. 10 are shown asextending downwardly within a tube 58 through the wheel assembly 41 andthrough the threaded element 67 upon which is mounted the wheel assembly41. The electronics facilities 59 which are attached to the lowerportion of threaded element 67 are shown on FIG. 7 but are not on FIG.10 for purposes of clarity.

The precision of the float device 30 is effected by two phenomena,hysteresis and damping. Hysteresis is defined as the "dead zone" withinwhich changes in fluid level are not registered by movement of thefloat. This is caused entirely by friction and angular momentum i.e.,friction of the wheel 60 against the tube 22 inner wall and angularmomentum of the rotating assemblies, friction of the bearings and othermovements. Due to the lightweight material used, the jeweled movementsand specialized TEFLON compounds used in the assembly, hysteresis of thefloat is minimized. In addition, the float is precision engineered to benearly critically clamped when offset from equilibrium. This is due toan exact volume displacement to weight ratio, allowing the float to cometo equilibrium within three oscillations. The described float has lowhysteresis and achieves a resolution greater than one ten thousandth ofan inch (0.0001 inch).

DESCRIPTION OF FIG. 16

FIG. 16 discloses further details of the upper portion of the probeassembly together with further details of how the probe processor 48 isaffixed to and mounted to this upper portion of the probe assembly. Theupper portion of probe segment 21 receives the lower threaded portion ofthe fill cap 7. The probe processor 48 is inserted from the bottom intosegment 21 with the bottom section of segment 21 having female threads(not shown) which screw into the threaded element 102 at the bottom ofprobe processor 48. A suitable O-ring or gasket affixed to the upperportion of ridge 104 forms an explosion tight seal for the probeprocessor 48 within probe segment 21. Below ridge 104, the inner portionof cylindrical surface 103 receives bracket 101 which onto its bottomportion is mounted a horizontal plate 99. This plate receives, by meansof a force fit, the infrared photo detector 47 and mounts the upperportion of spring 46. Spring 46 prevents the float 30 and the upper cone42 from crashing into the photo detector 47 while probe 4 is beinghandled during deployment or if fluid level should rise such to causefloat 30 to rise and force cone 42 against photo detector 47. Suitablewires interconnect the infrared photo detector with the probe processor48. These wires are indicated as dotted lines on FIG. 16 and whichextend through cylindrical element 103 and the threaded element 102. Aspriorly mentioned, the photo detector 47 receives the coded signalstransmitted upwards from the infrared LED 43 with the digital signalsrepresenting fluid level within the tank. Infrared photo detector 47 andinfrared light emitting diode 43 are conventionally available from TRWOptron Electronics of Dallas, Tex. as part numbers OP913 and OP295respectively. The cylindrical surface 103 is inserted into the upperportion of probe segment 22 and is affixed to probe segment 22 by meansof screw 105. The opening 28 receives the upper temperature sensingstrip 36 and the lower temperature sensing strip 27 to mate connector101B with connector 101A whose wires are indicated as dotted lines onFIG. 16 and which extend through cylindrical element 103 and thethreaded element 102 and connect with the probe processor 48. Theconductors associated with the temperature sensing element 29 on thesetwo strips are thereby connected to the probe processor 48 so that theprobe processor may include in the data it generates the completestratification of temperatures of the tank fluid as well as the vaporabove the fluid. Stratified temperatures of the complete length of theprobe assembly includes: the fluid, the vapor in the fill pipe and theearth surrounding the surface above the tank at the fill pipe manhole 8.

DESCRIPTION OF FIG. 17

FIG. 17 comprises a view of the upper portion of the probe processor 48after it is extended into the probe segment 21 and prior to the timethat the fill cap 7 is screwed into the upper portion of probe segment21. As shown on FIG. 17, a switch 106 is provided to activate the probeprocessor by turning it from off to an on position. The plug 107 isprovided to permit an interconnection between the probe processor andthe field processor mounted in the technician's truck. These connectionsprovided by plug 107 permit the technician to activate and initializethe probe processor at the beginning of a test as well as to transferthe data collected during a test from the memory of the probe processorto the portable field processor.

DESCRIPTION OF FIGS. 18, 19 AND 20

FIG. 18 shows the field processor which is connectable with the probeprocessor 48. This connection is established by means of a cable thatruns from the field processor of FIG. 18 to plug 107 of the probeprocessor. The field processor is generally designated as one element108 and is mounted within a suitable carrying case 109 and furtherincludes handles 110 as shown on FIG. 18.

FIG. 19 shows further details of the field processor. As can be seen,the field processor comprises a frame 111, including handles 110 and aremovable base plate 116 together with associated equipment mounted onthe base plate 116. This equipment includes a power supply 112,batteries 121 and an assembly 113 for mounting the printed wiring boardscomprising the field processor. Cables 114 and 115 interconnect thevarious portions of the field processor together.

FIG. 20 discloses further details of the keys and push buttons mountedon the display portion or top plate 117 of the field processor. As canbe seen on FIG. 20, the top plate or control panel of the fieldprocessor comprises an LCD display 118 together with a plurality ofcontrol buttons 119.

The field processor is activated by turning on a control switch 120 andby then operating the various keys 119 of FIG. 20 to achieve the desiredresults. The operation of field processor is analogous to that of anycurrently available program controlled processor and therefore need onlybe described briefly. It is expressly understood that the fieldprocessor may in fact be substituted with such portable computers forexample as: the Toshiba Model #1100, Kaypro Model #2000, or theIBM/Model PC Convertible. Any such conventionally available machineswith easily obtainable industrial control software may suit the purposeof the so called field processor 108. The SETUP key is activated to setup or initialize the probe processor at the beginning of a test toinclude the self test operational routines. The RETRIEVE key isactivated to retrieve data from the probe processor at the conclusion ofa test. The OFFICE key is activated when data is to be transmitted fromthe field processor over a phone line or the like to an office computer.The HELP key is depressed whenever the field technician requiresassistance in operating the field processor such as the manual stickmeasurement of the tank. The NUMERICAL DIGIT keys 0 through 9 are usedto enter numerical data into the field processor such as the manualstick measurement of the tank. The YES and NO keys are used to provideanswers to questions displayed on the LCD display 118 of the fieldprocessor. The ENTER key is depressed to enter data or commands into thefield processor such as the manual stick measurement of the tank. TheNEXT key is depressed to advance to the next program sequence. TheBACKSPACE key is depressed to step backwards to correct error when usingthe 0 through 9 keys, etc. The ARROW keys are depressed to permit thefield processor to return to a prior program sequence or advance toother program sequences.

It is also contemplated by the present invention to allow the fieldprocessor to load the probe 4 test data on to a conventional floppymemory disk so as to permit the transfer of test data to be mailed tothe processing center for analysis in cases where telephonecommunications are not practical or convenient.

DESCRIPTION OF FIG. 21

FIG. 21 discloses further details of the float processor 59. In theupper lefthand corner of FIG. 21, the rotation of shaft 78 causes codewheel 57 to rotate and to interrupt a light beam which passes throughthe elongated slot opening 70 on code wheel 57 which is positionedwithin the U-shaped opening in the lower portion of decoder device 56.The U-shaped opening in device 56 is clearly shown on the top part ofFIG. 7. Code wheel 57 and the decoder device 56 are commerciallyavailable components and have been identified in detail priorly in thisspecification.

The output signals of decoder device 56 are applied to its pins 85. Pins85 engage connector 86 which is attached by means of the wires of cable53 to the two channel buffer circuit 125 of the float processor 59. Theoutput of buffer 125 is connected over path 126 to microprocessor 127.

Battery 128 provides power for the float processor 59 in theconventional manner. The power is applied to the float processor afterswitch 124 is turned to the ON position. At that time, battery power isconnected over path 129 to the float power supply and voltage monitoringcircuit 130 which, in turn, applies power over path 131 to themicroprocessor 127. Element 130 is a conventional circuit whose purposeis to indicate energy levels of battery 128 when processor 127interrogates element 130. Timing is provided to the float processor bymeans of the crystal timing circuit 132 which is connected over line 133to the microprocessor 127. This provides for precision timing to themicroprocessor 127.

The output of the microprocessor 127 is applied over path 134 to the "G"terminal of the field effect transistor (FET) 135. The "S" element ofthe FET is grounded at 136. The "D" element of the FET is connected viaone wire of path 61 to the infrared LED 43. The other wire of path 61 isconnected via resistor 138 to the plus battery voltage. The FET device135 is commonly available and is identified as a part number in VN0104.

In operation, the code wheel 57 rotates as it responds to changes in thelevel of the tank fluid 3. This rotation of code wheel 57 interrupts thelight beam within the decoder device 56 to produce two channels of datarepresenting (1) the number of times the light beam has been interruptedand (2) an indication as to the direction of rotation in which the codewheel 57 is turning. The wave form outputs of the buffer 125 on path 126are subsequently described in detail in connection with FIGS. 22, 23,and 24.

The microprocessor 127 counts the number of interruptions of the sensedlight beam and amplifies the wave forms representing these interruptionsas is subsequently described. Amplifies in this meaning refers to the"quadrature effects" as represented in FIG. 24. The sensed level data isrepresented in the form of pulsing the infrared LED 43. This creates anoptical communication link which is transmitted upwards within the probetube 22 to the probe processor 48 via the infrared path 44 shown on FIG.5.

Although in the preferred embodiment all data generated by the probe 30and the probe processor 59 is up-linked via the infrared beam 44 so theprobe processor 48 can store the up-linked data for further analysis, itshould be expressly understood that the float processor 59 can, ifdesired, include means of storing digital signal processing in such analternative embodiment. In this embodiment, the float processor 59 maybe most useful in permanently installed probe 4 devices. In such anembodiment, the float processor 59 can by itself perform extensivedigital signal processing. In addition, it is also to be understood thatwithin this alternative embodiment, an analysis of level, temperatures,and barometric pressures may occur within the probe processor 48 itselfrather than being uploaded to external computers.

DESCRIPTION OF FIGS. 22, 23, AND 24

FIGS. 22, 23, and 24 disclose the wave forms which are produced by theencoder device 56 in the form of signals applied to path 53. The decoderdevice 56 generates two output wave forms. These two wave forms aredesignated as channel (CH) A and channel (CH) B on each of FIGS. 22, 23,and 24. Channel A is identified by the reference numeral 145 whilechannel B is identified by the reference numeral 146 on each of FIGS.22, 23, and 24.

In FIG. 22, the channel A wave form is shown as leading the channel Bwave form at the time represented by the dotted line 147. FIG. 22 isthereby indicative of the code wheel 57 rotating counter clockwise inresponse to a lowering of the tank fluid 3. Conversely, in FIG. 23, thechannel B wave form 146 is advanced over that of the channel A wave form145 at the time represented by dotted line 147. This condition isindicative of a clockwise rotation of the code wheel and a rising of thetank fluid 3.

Microprocessor 127 digitally amplifies the signals of FIGS. 22 and 23 asshown in FIG. 24. FIG. 24 discloses the digital amplification. Here aclock signal 152, a channel A signal 145, and a channel B signal 146 arerepresented. It further shows these signals being divided time wise bythe vertical dotted lines identified as elements 147 through 151. Thechannel A signal 145 between times 147 through 151 represents the outputsignal for channel A caused by a single interruption of the light beamthrough a slot 70 of code wheel 57 moving in a counter clockwisedirection. At time interval 148, the value of the channel A signal 145is compared to the value of the channel B signal and an output signal isgenerated under control of the clock signal 152 to produce a digitalvalue of 1 as indicated by the reference numeral 153. Similarly, as timeintervals 148, 149, 150, and 151 coincide with the channel A and Bsignals 145 and 146 and the processor clock signal 152, themicroprocessor 127 generates an output signal indicating the digitalvalues of 2, 3, and 4 as represented by the reference numerals 154, 155,and 156 respectively. This digital amplification process is generallyknown in the art as quadrature signal processing.

In operation, the microprocessor 127 can sectionalize or divide eachsignal 145 and 146 into four separate and distinct signals asrepresented by the digits associated with reference numerals 153 through156. Thus, by means of this quadrature signal processing, the processorcan determine from a comparison of the channel A and channel B signalswhich signal is leading and thereby determine whether the tank fluid isrising or lowering. Further, by means of the quadrature signalprocessing, the microprocessor 127 can determine which quadrant of acycle to which the code wheel has rotated. This increases the accuracyof the probe and thereby allows the indications of changes in fluidlevel to be determined with greater precision.

DISCUSSION OF FIG. 25

FIG. 25 discloses further details of the operation of the floatprocessor 59. Upon act of the power switch 124 of the float processor onFIG. 21, a self diagnostic routine 165 on FIG. 25 is initiated bymicroprocessor 127 (FIG. 21). This diagnostic routine 165 automaticallychecks out the operation of all the electronics and associated equipmentof the float processor 59. Included in the things that are tested arebattery voltage. The process advances from element 165 on FIG. 25 toelement 166 which determines whether or not all of the tested criteriaof the float processor tests okay. If the answer is YES, the processadvances to element 167 which gets a signal from the input bufferelement 125 of FIG. 21. The data acquired from the buffer 125 ispresented to element 168 of FIG. 25 which makes a determination as towhether or not the acquired data represents new data or represents datathat is unchanged from the previous reading. If the answer of element168 is NO, then the old data that was recently read from buffer 125 isapplied to element 169 which controls processor 59 so that the old datais then applied via the field effect transistor 135 to infrared LED 43for transmission upward on the infrared beam to the probe processor 48.

If the element 168 makes a YES determination indicating that theacquired data is new data, then the process advances to element 170which determines whether channel A does or does not lead channel B asshown on FIGS. 22 and 23. The process then advances either to element171 or 172 depending on the answer generated by element 170. If thefluid level is rising, then channel A leads channel B and the processadvances over the YES output of element 170 to element 171 whichincrements a level counter within the microprocessor 127. On the otherhand, if the level of the tank fluid is falling, then channel B leadschannel A and the process advances over the ELSE output of element 170to element 172 which decrements the level counter within themicroprocessor.

The process then advances either from blocks 171 or 172 to the element169 which transmits the new change in fluid level information via theinfrared LED in the infrared beam to the probe processor as priorlydiscussed. Each time that element 169 causes data to be transmitted, thedata is transmitted over the infrared beam 44 and indicates either thatthe fluid level has not changed or, if it has changed, that it haseither risen or has lowered. The process then advances from element 169over path 173 back to the element 166 which begins a new cycle. Also, ifthe NO output of element 166 is activated at any time, the processadvances directly from the NO output of element 166 to element 169 whichtransmits information up on the infrared beam indicating that thediagnostic routine did not properly run.

DESCRIPTION OF FIG. 26

FIG. 26 discloses further details of the probe processor 48. Uponactivation of the power switch 106 for the probe processor, the selfdiagnostic routine 180 automatically checks the operation of the variouselements of the processor and further checks out various systemparameters such as battery voltages. If all of these check "ok" byelement 181, the process advances over the YES output of element 181 toelement 184. If some parameter does not check "ok", the process advancesout over the NO output to element 182 which transmits information to thefield processor 108 indicating that the probe processor is not fullyoperable. The process then ends in element 183.

In element 184, the probe processor receives a down-load program 201from the field processor. The down-load program 201 comprises theprogram routines that the probe processor is to execute in the preferredembodiment of the invention.

The process next advances from element 184 to element 185 whichcomprises the first step in the execution of the down-loaded program 201that the probe processor receives from the field processor. In element185, the process waits for the reception of a "start run" command. Thiscommand is included in the down-loaded program received from the fieldprocessor and could indicate various alternative start times. First ofall, it can indicate an immediate start time for the START RUN command.It can also include a time delay of a predetermined amount of time forthe beginning of the START RUN command. Also, it can include apredetermined default START RUN command time. In any case, if theindicated time to start does not equal "NOW?", the routine loops back toitself over path 198. When the question of element 185 is satisfied, theelement causes the process to advance out over the YES output to element186. In process 186, the probe processor gets the liquid level datawhich is received at the infrared photo detector 47 via the infraredbeam 44 which is transmitted up from the float processor 59 to the probeprocessor as described priorly in connection with the description of theflow chart of FIG. 25. The process then advances from element 186 toelement 187 which reads the multiple temperature information from thetemperature sensors 29 located throughout the length of the probe 4 onthe strips 27, 36, and 38. The process then advances from element 187 to188 which enters the barometric pressure information into the probeprocessor. The process then advances from element 188 to element 189which causes the values derived by elements 186, 187 and 188 to bestored in a short term memory for subsequent digital signal processing.

The process next advances from element 189 to element 190. Element 190keeps track of how many times the probe processor has performed the taskassociated with elements 186, 187, and 188. If the count equals apredetermined number (such as 30 in the preferred embodiment), the YESoutput of element 190 is activated and the process advances from element190 to element 191. On the other hand, if the count is less than 30,then the process advances out over the NO output and loops back to theinput of element 186 where the above described sequence is performedonce again by elements 186, 187, 188, and 189 until such time as thecount determined by element 190 does equal 30.

In routine 191, the probe processor performs digital signal processingon the 30 different saved values stored in the short term memory of theprobe processor in connection with element 189. The details of thissignal processing have been priorly described. The values which resultfrom the execution of process 191 are stored in the probe processormemory by element 192 for subsequent upload and transfer to the fieldprocessor. The process next advances from element 192 to element 193.Element 193 monitors either the termination of a specified period oftime for the tests, or the utilization of the maximum amount ofavailable memory to store the test data. In connection with this, itasks the question as to whether the recording of data should beterminated. If the answer is NO to this question, the process returns tothe beginning of element 186 over path 200 which causes theabove-described sequence to be repeated one or more times. If the answerto the question asked by element 193 is YES, the process advances outover the YES output of element 193 to element 194. Element 194determines whether or not the stored data generated by element 192should be uploaded and transferred to the field processor at this time.If, at this time, the field processor is not available and connected tothe probe processor, the answer to the question is NO and the processloops back over path 199 to the input of element 193 and the functionsperformed by elements 193 and 194 are repeated until such time as thefield processor is available and connected to the probe processor. Thisconnection is made via plug 107 as priorly described. When theconnection is made, the probe processor is requested to upload itsstored information to the field processor. At this time, the YES outputof element 194 is activated and the process advances to element 195which increments a usage counter within the probe processor by one. Theprocess then advances to element 196 which causes the stored informationin the probe processor to be transferred to the field processor aspreviously discussed in connection with element 192. The process is nowcomplete when it advances from element 196 to element 197.

It is to be expressly understood that it is contemplated, in accordancewith the present invention, that the probe processor program 201 couldcause element 192 to be uploaded at the completion of each data pointprocessed by element 191. This would be particularly useful in a "realtime" embodiment of the invention which would display the test by thefield processor 108 where the cable between the field processor 108 andthe probe processor 48 is kept connected through the use of a specialfill pipe cap 7 which has the capacity to receive the cable. Such realtime observation of tank behavior is useful to demonstrate to the tankowner/operator the effectiveness of the tank testing probe. It is alsouseful in any other situation in which it is desirable that real timeinformation pertaining to the tank leakage be made instantaneouslyavailable for any reason whatsoever.

While preferred embodiments of the present invention have been shown, itis to be expressly understood that modifications and changes may be madethereto and that the present invention is set forth in the followingclaims.

I claim:
 1. A method of determining information including informationindicating the leakage of liquid in storage tanks, said methodcomprising the steps of:inserting self contained measuring apparatusinto a tank whose leakage is to be measured, operating said apparatus toobtain a plurality of data readings at different times indicating theinstantaneous tank liquid level at the time of each reading, storing thedata collected during each reading in said apparatus, subsequentlyconnecting said apparatus to a computer, transferring said stored datafrom said apparatus to said computer, and operating said computer toprocess said data to determine the leakage rate of said tank.
 2. Themethod of claim 1 wherein said tanks have fill pipes and wherein saidmethod further comprises the steps of:inserting said apparatus in saidtank so that the entirety of said apparatus is below the top of the fillpipe of said tank, and inserting a fill pipe cap on said fill pipe. 3.The method of claim 2 wherein said cap is a locking type cap.
 4. Themethod of claim 1 in combination with the steps of:operating saidapparatus to sense the temperature at different strata within said tank,recording data indicating the temperature sensed for each strata, andtransferring said temperature data together with said stored liquidlevel data to said computer for use by said computer in determining saidtank leakage information.
 5. The method of claim 4 in combination withthe steps of:operating said apparatus to sense barometric pressureinformation, recording said pressure information in said apparatus, andtransferring said recorded barometric pressure information to saidcomputer together with said temperature data and said stored liquidlevel data for use in determining said tank leakage information.
 6. Amethod of determining information including information indicating theleakage of liquid in storage tanks, said method comprising the stepsof:inserting self contained measuring apparatus into a tank whoseleakage is to be measured wherein said inserted apparatus comprises avertically oriented hollow tube, a probe processor in the upper portionof said tube, and a float including a float processor suspended in saidliquid in the lower portion of said tube, operating said float processorto generate a plurality of data readings at different times indicatingthe instantaneous tank liquid level at the time of each reading,transmitting said data for each reading from said float processor tosaid probe processor, recording the transmitted data for each reading insaid probe processor, subsequently removing said apparatus from saidtank, connecting said probe processor to a computer, transferring saidstored data from said probe processor to said computer, and operatingsaid computer to process said data to determine the leakage rate of saidtank.
 7. The method of claim 6 wherein said step of transmittingincludes the steps of:encoding said generated data readings into anencoded optical signal, transmitting said optical signal upwards withinsaid tube, receiving said optical signal by a photo detector, andapplying a signal representing said generated data from said detector tosaid probe processor.
 8. The method of claim 7 in combination with thesteps of:operating said probe processor to sense the temperature atdifferent strata within said tank, recording data indicating thetemperature sensed for each strata, and transferring said temperaturedata together with said stored liquid level data to said computer foruse by said computer in determining said tank leakage information. 9.The method of claim 8 in combination with the steps of:operating saidapparatus to sense barometric pressure information, recording saidpressure information in said apparatus, and transferring said recordedbarometric pressure information to said computer together with saidtemperature data and said stored liquid level data for use indetermining said tank leakage information.
 10. Self contained measuringapparatus adapted to be inserted into a tank whose leakage of storedliquid is to be measured, said apparatus comprising:means for obtaininga plurality of data readings at different times indicating theinstantaneous tank liquid level at the time of each reading, means forstoring said data collected during each reading in said apparatus, meansfor subsequently connecting said apparatus to a computer, and means fortransferring said stored data from said apparatus to said computer, saidcomputer being operable to process said data to determine the leakagerate of said tank.
 11. The apparatus of claim 10 in combinationwith:means for sensing the temperature at different strata within saidtank, means for recording data indicating the temperature sensed foreach strata, and means for transferring said temperature data togetherwith said stored fluid level data to said computer for use by saidcomputer in determining said tank leakage information.
 12. Selfcontained measuring apparatus adapted to be inserted into a tank whoseleakage of stored liquid is to be measured wherein said insertedapparatus comprises a vertically oriented hollow tube, a probe processorin the upper portion of said tube, and a float including a floatprocessor suspended in said liquid in the lower portion of said tube,said apparatus further comprising:means for operating said floatprocessor to generate a plurality of data readings at different timesindicating the instantaneous tank liquid level at the time of eachreading, means for transmitting said data for each reading from saidfloat processor to said probe processor, means for recording thetransmitted data for each reading in said probe processor, and means forconnecting said probe processor to a computer for the transfer of saidstored data from said probe processor to said computer, said computerbeing operable to process said data to determine the leakage rate ofsaid tank.
 13. The apparatus of claim 12 wherein said means fortransmitting includes:means for encoding said generated data readingsinto an encoded optical signal, means for transmitting said opticalsignal upwards within said tube, means for receiving said opticalsignal, and means for applying a signal representing said generated datafrom said detector to said probe processor.
 14. Apparatus fordetermining information including information indicating the leakage ofliquid in a storage tank, said apparatus comprising:a probe processor inthe upper portion of said tank, a float suspended in said liquid, afirst means on said float for determining the instantaneous level ofsaid tank liquid, a second means on said float for transmitting data tosaid probe processor representing said determined fluid level atsuccessive times, said probe processor being operable for recording saidtransmitted level data, and means for transferring said recorded datafrom said probe processor to an external computer to determine said tankleakage rate from said transferred data.
 15. The apparatus of claim 14in combination with:means for sensing the temperature within said tankat different strata within said tank, said probe processor beingoperable for recording data indicating the temperature sensed for eachstrata, and means for transferring said recorded temperature data alongwith said stored liquid level data to said computer for use indetermining said tank leakage information.
 16. The apparatus of claim 15wherein said probe processor is operable for sensing and recordingbarometric pressure information, said apparatus further comprising meansfor transferring said recorded barometric pressure information to saidcomputer together with said recorded temperature data and said storedliquid level data for use in determining said tank leakage information.17. Apparatus for determining information including informationindicating the leakage of liquid in a storage tank, said apparatuscomprising:a hollow probe tube suspended vertically in said tank with atleast a lower portion of said probe tube being immersed in said liquidin said tank, a probe processor and a receiver in the upper innerportion of said tube, a float suspended below said probe processor insaid liquid within said tube, encoder means mounted on said float withinsaid tube for determining the instantaneous level of said tank liquid, afloat processor mounted on said float within said tube and responsive tosaid determination by said encoder means for transmitting data to saidreceiver representing said liquid level at successive times, said probeprocessor being operable for recording said transmitted level data, andmeans for transferring said recorded data to an external computer todetermine said tank leakage.
 18. The apparatus of claim 17 wherein saidfloat comprises:centering means for positioning said float within thecenter of said tube and away from the inner surface of said tube whilepermitting said float to move vertically with low hysteresis in responseto changes in tank fluid level.
 19. The apparatus of claim 18 whereinsaid centering means comprises:a first vertically oriented memberaffixed to the bottom of said float, a plurality of vertically orientedwheels affixed by spring loading means to said member and radiallyspaced from each other about the vertical axis of said member, each ofsaid wheels bearing under control of said spring loading means againstthe inner surface of said tube to center the lower portion of said floatwithin said tube, a second vertically oriented member affixed to the topportion of said float, a plurality of spring loaded vertically orientedwheels affixed by spring loading means to said second member andvertically spaced from each other about the vertical axis of saidmember, each of said wheels bearing under control of said spring loadingmeans against the inner surface of said tube to center the upper portionof said float within said tube while maintaining contact between saidfriction wheel periphery and the inner surface of said tube.
 20. Theapparatus of claim 19 in combination with a first spring fixed to thelower portion of said first vertical member and a second springpositioned above said float to cushion said float against largemagnitude downward and upward vertical shocks.
 21. The apparatus ofclaim 19 wherein said encoder means comprises:a data transducer, a codewheel having radial slots for sequentially interrupting and enabling ahigh beam generated by said transducer as said code wheel rotates inresponse to changes in fluid level, and means responsive to saidinterruption for generating output data indicating the direction andamount of rotation of said code wheel.
 22. The apparatus of claim 21 incombination with:an infrared beam generator, means for applying outputsignals from said float processor to said infrared generator forgenerating a coded infrared beam containing said data that istransmitted to said receiver, and means in said receiver for receivingand decoding said infrared beam to derive said transmitted data.
 23. Theapparatus of claim 19 in combination with:means for operating saidapparatus to sense the temperature at different strata within said tank,means for recording data indicating the temperature sensed for eachstrata, and means for transferring said temperature data with saidstored liquid level data to said computer for use by said computer indetermining said tank leakage information.
 24. The apparatus of claim 23in combination with:apparatus for operating said apparatus to sensebarometric pressure information, means for recording said pressureinformation in said apparatus, and means for transferring said recordedbarometric pressure information to said computer together with saidtemperature data and said stored liquid level data for use indetermining said tank leakage information.
 25. A method of determininginformation including information indicating the leakage of liquid instorage tanks, said method comprising the steps of:inserting selfcontained measuring apparatus into a tank whose leakage is to bemeasured, operating said apparatus to obtain a plurality of datareadings at different times indicating the instantaneous tank liquidlevel at the time of each reading, transmitting information representingsaid data readings over an infrared beam from a lower portion to anupper portion of said apparatus, storing the data transmitted over saidinfrared beam in said apparatus, subsequently connecting said apparatusto a computer, transferring said stored data from said apparatus to saidcomputer, and operating said computer to process said data to determinethe leakage rate of said tank.
 26. Self contained measuring apparatusadapted to be inserted into a tank whose leakage of stored liquid is tobe measured, said apparatus comprising:means for obtaining a pluralityof data readings at different times indicating the instantaneous tankliquid level at the time of each reading, means for transmittinginformation representing said date readings over an infrared beam from alower to an upper portion of said apparatus, means for storing said datatransmitted over said infrared beam in said apparatus, means forsubsequently connecting said apparatus to a computer, and means fortransferring said stored data from said apparatus to said computer.